WO1992017289A1

WO1992017289A1 - Method and system for degreasing solid objects

Info

Publication number: WO1992017289A1
Application number: PCT/US1992/002723
Authority: WO
Inventors: Gene C. Weitz
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-04-08
Filing date: 1992-04-03
Publication date: 1992-10-15
Anticipated expiration: 1993-10-08
Also published as: AU1901992A

Abstract

A degreasing method and system which subjects dirty and oily parts to a bath of relatively impure solvent (20) and thereafter rinsing such parts in relatively pure solvent (68). The relatively pure solvent is continuously obtained by distilling a portion of the unique solvent in a closed continous flow system (34). The solvent used is a mixture of esters of low molecular weight aliphatic carboxylic acid and normally liquid branched chain alkane.

Description

METHOD AND SYSTEM FOR DECREASING SOLID OBJECTS

DESCRIPTION AND BACKGROUND OF THE INVENTION

This invention relates to a liquid phase degreasing method, a system and apparatus, and solvent therefor.

A variety of lubricants, including petroleum products, water soluble oils and synthetic or se isynthetic fluids are employed in metal working and in the repair of metallic objects such as automobile parts. Some of these fluids pose difficult problems for removal of these contaminants from the surface of the objects. Many of these problems are associated with environmental concerns both from an atmospheric pollution and waste disposal standpoint.

The prior art solutions to these cleaning problems have been directed to vapor degreasers using chlorinated solvents such as 1, 1, 1-trichloroethane, trichloroethylene, perchloroethylene or methylene chloride. The term "degreaser" is a term of art for removing all manner of contaminants from solid surfaces such as oil, grease, welding flux, water surfactants, metal salts and the like.

However, the prior art vapor degreasers pose significant environmental problems. The chlorinated solvents frequently break down and form corrosive hydrochloric acid in the presence of water. The vapor phase operation causes expensive vapor recovery systems to be used without which there would be significant atmospheric pollution. For example, Barday's U.S. Patent No. 3,460,990 illustrates the complicated means needed in a closed system to operate a vapor degreasing method.

It is thus apparent that a need exists for a degreasing method and system which minimizes the dangers of waste disposal and atmospheric pollution in a simple cost effective manner. Summary of the Invention According to the present invention, the liquid degreasing method and system subjects contaminated objects, such as automobile parts, to a bath of relatively impure cleaning solution or solvent in an open system and thereafter rinsing the objects with a liquid spray of relatively pure cleaning solution or solvent. The relatively pure solvent is obtained in continuous fashion by distilling a portion of the relatively impure solvent and returning the distillate to the spray means for use in the rinse cycle. The cleansed objects are thereafter dried within the open system by forced hot air which also acts as a diluent to any vaporous material escaping the open system.

In an embodiment of the invention, the method of degreasing the surface of solid objects comprises the steps of:

(a) immersing an object in a liquid bath comprising a relatively impure solvent selective for the contaminants;

(b) removing the object from the immersion bath;

(c) subjecting the object to a liquid spray wash comprising relatively pure solvent selective for the contaminants;

(d) contacting the object with a gaseous drying medium;

(e) continuously removing a portion of the relatively impure solvent from the bath of step (a) and purifying such removed portion by distilling therefrom relatively pure solvent; and

(f) returning the distilled relatively pure solvent to the spray wash of step (c) .

In another embodiment of the invention, a system for degreasing the surface of solid objects comprises:

(a) a unitary vertically disposed elongated chamber open to the atmosphere containing a liquid bath zone in the lowermost portion of the chamber, a liquid rinse zone immediately above the liquid bath zone, and a gaseous drying zone at the uppermost portion of the chamber above the rinse zone;

(b) liquid purification means comprising a distillation zone connected to the liquid bath zone in order to receive a portion of the liquid bath and connected to the rinse zone in order to provide a source for liquid rinse;

(c) means connected to the gaseous drying zone for supply of drying medium thereto; and

(d) means for vertically transporting objects to and through the bath zone, the rinse zone, and the drying zone, respectively.

A further embodiment of the system includes means for vertically transporting objects which comprises a object container basket resting on a tray support means movably connected to means suitable for vertical movement, up and down, of the tray within the system.

Another embodiment of the invention is a degreaser solvent comprising a mixture of esters of low molecular weight aliphatic carboxylic acid and a normally liquid branched chain alkane.

Solvents which are preferred in the practice of this invention are broadly esters with a co-solvent such as an isoparaffin, i.e., a normally liquid branched chain alkane, having from 5 to 20, preferably from 11 to 14 carbon atoms per molecule *^•having a boiling range from 450 *F to 550*F, e.g., from 475 *F to 530^λF. Such solvents are preferable to the prior art halogenated, olefinic and/or aromatic solvents which pose environmental concerns. Typically, the solvents useful in the practice of this invention will be (i) those with a flash point of 140^lF-160*F TCC, and (ii) those at a higher range of from 190'F-260^XF TCC. It is distinctly preferred that the selective solvent be a mixture of components having substantially the same boiling range, so that the system will be operational over a wide range of inventive solvent mixtures. The compositions of the invention have good wetting ability and solvency power with minimum stable emulsifying tendencies.

The preferred isoparaffin is an isomer or mixture of isomers of dodeσane although other isomers from decane through hexadecane are also useful in the practice of this invention. 4-methyl-3, 3-diethyl-l-5-isopropyloctane (IϋPAC name) is particularly desirable as a co-solvent. Another useful co-solvent is a tridecane having a boiling range from 430 F - 470^ΛF. It is preferred that the normally liquid branched chain alkanes for use in this invention have a flash point (TCC ^VF) of at least 240^λF and a boiling range from 486⁴F to 522*F. Its seleσtiveness for compounds of low polarity make those normally liquid branched chain alkanes attractive as a co-solvent in the inventive cleansing composition.

The primary solvent of this invention comprise esters of low molecular weight aliphatic carboxylic acids. Carboxylic acids having from 2 to 16 carbon atoms, prefer-ably 11 to 14 carbon atoms per molecule are deemed herein to be relatively low molecular weight. These can be either straight chain or branched-chain acids or mixtures thereof in admixture with the alkane co-solvent. Typically, these acids are converted into its ester by well-known reactions such as reaction with an alcohol or via the acid chlorides. The carboxylic acid is converted directly into an ester when heated with an alcohol in the presence of a little mineral acid, such as concentrated sulfuric acid. A particularly preferable ester is the -keto ester such as ethylaσetoacetate. Other particularly useful esters include octylacetate and deσylacetate. It is preferred that the ester solvent component of this invention be an oxoalcohol-branched ester having a flash point (TCC ^lF) of at least 260^lF and a boiling range from 464 F to 545 F. The solvent composition of the present invention have desirable characteristics such as non-toxicity, relatively high flash point, high solvency, and low environmental impact which enhance their usefulness under a variety of circumstances. These relatively low molecular weight aliphatic carboxylic acid esters together with normally liquid branched chain alkanes provide the desired characteristics of contaminant solvency, and low toxicity relative to halogenated hydrocarbons as well as having a relatively high flash point. Moreover, the present compositions do not have a harmful effect on the earth's stratospheric ozone layer; depletion of the ozone layer is another problem which is encountered with the use of halogenated hydrocarbons. Further, esters of the present invention generally have a relatively low vapor pressure, and are, therefore, less volatile, providing the advantage of lower volatile organic compounds pollutant emissions, than prior art composition.

Care should be taken in solvent selection so that explosive mixtures may be minimized in the open system of this invention.

The primary solvent component of the present inventive solvent composition has the formula

(R₁)OOC(R₃)C00(R₂) wherein R, and R_ are C . - C_β alkyl, and may be same or different, and R, is -(CH₂) -, wherein n is an integer from 2 to 8. Preferably n is 2, 3 or 4. Examples include ethyl adipate, dimethyl adipate, dimethyl glutarate, or any combination thereof.

Other esters with longer chain alkyl groups derived from alcohols, such as ethyl, propyl, isopropyl, butyl, amyl, and oxyl and mixtures thereof including methyl, can be employed with satisfactory results. Preferably the ester obtained from the oxylalcohol is preferable. Also the acid portion of these esters can be derived from other lower and higher molecular weight dibasic acids, such as oxalic, malonic, pimelic, suberic, and azelaic acids and mixtures thereof. These and other esters can be employed provided they are mutually soluble with the alkane co-solvent, are not classified as flammable liquids (Flash Point at or above 140^lF by Tag Closed Cup method) and have at least 2.0 wt. % solubility in water at 77*F. The concentration or ratio of alkane to ester is not considered critical and the percentage of the two components can vary with wide ranges such as from 50 to 95% alkane and conversely 5 to 50% ester on the basis of the weight percent of those two components only to increase and decrease solvency. A 50/50 mixture would not be uncommon.

Examples of the inventive solvent blends may include a relatively low boiling blend or a relatively high boiling blend depending upon the needs of the individual user of the method and system, such as

Relatively low boiling blend

Component Volume Description Boiling Range Percent f%) octylacetate 5 - 95 Acetic acid ester 340^lF-420^lF

Ooff CCyy--CCgg bbranched oxoalcohol

Isoparaffin 95 - 5 Aliphatic hydrocarbon 370*F-410^VF mixed of ^{of c}10^-c14 c₁₁-c₁₄

B. Relatively hiσh boilinσ blend decylacetate 95 Acetic acid ester 430^VF-480^ΛF of Cg-C₁₁ branched oxoalcohol tridecane 95 - 5 Aliphatic hydrocarbon 430*F-470*F ^{of C}12^~C15

Similar results may be obtained by using even higher boiling range components such as an isoparaffin having a boiling range from 486*F to 522'F and an oxoalcohol branched ester having a boiling range from 464^λF to 545*F.

The useful cleansing compounds of the present invention are insoluble or, preferably, very slightly soluble in water, and may also be somewhat viscous. Therefore, in practice, the compositions may contain emulsifying surfactants in combination with the esters and alkanes. These emulsifying surfactants are nonionic, anionic, cationic or amuphoteric surfactants; preferably, nonionic surfactants such as the condensation products of alkylene oxides, for example ethylene oxide, with any of the variety of hydrophobic morities. Examples include ethoxylated aliphatic alcohols, ethoxylated alkylphenols, ethoxylated amines, amides, and the like. Generally, the added emulsifying agent will range on a weight basis from about 0-20% of the composition. In a preferred embodiment, the inventive composition comprises a mixture of dimethyl edipate, dimethyl succinate, and dimethyl glutarate in a total amount of about 40%-60%, a mixture of 4-methyl-3, 3-diethyl-5-isopropyloctane and an isomeric hexadecane (50-50) in a total amount of from 50%-30%, and an ethoxylated aliphatic alcohol, in a total amount of about 0-10%.

The ester-isoparaffin-emulsifier composition may be used full strength or, in certain applications, diluted with water to a low as about 2% by volume concentration. Full strength solvency without water or emulsifying agent and which behaves as an azeotrope is particularly preferred.

Brief Description of the Drawing Further details and advantages of the present invention will be apparent from the description and accompanying drawing where the drawing illustrates one embodiment of this invention. Description of the Preferred Embodiment Reference is now made to the drawing which illustrates schematically one embodiment of the system of this invention for degreasing solid objects, such as automobile parts. The system includes a vertically disposed elongated chamber 100 open to the atmosphere. The lowermost portion 22 of the chamber is an immersion zone, the middle portion 18 of the chamber is the rinse zone, and the uppermost portion 30 is the gaseous drying zone.

Dirty and oily objects such as automobile parts (not shown) are manually placed into basket 10 which is supported on tray 12 and lowered into the chamber 100, for example, using cable connection 14 operating through pulley system 16. Other means (not shown) may be used in moving the tray 12 within the system such as hydraulically or electrically operated mechanical scissor means. Immersion zone 22 of chamber 100 contains an appropriate solvent 20 which is selective for the dirt and oil on the surface of the object. The cleaning solution in the bath, after use, is never absolutely free of greases and oils. The amount of contaminants within the cleaning composition need only remain below that level at which the solution loses its effectiveness. It has been found that immersion in a relatively impure cleaning solution followed by a rinse of relatively pure cleaning solution achieves superior results over immersion in relatively pure solution alone. The time for immersing the objects in the zone 22 depends considerably on the degree to which its surface is contaminated with oil and grease. Typically, immersion times from 1-2 minutes to 30 minutes or more, more typically, 5-10 minutes of immersion in zone 22.

Preferably, the liquid in immersion zone 22 is agitated through effective means such as ultrasonic transducer vibration means shown at 21 or through circulation of the fluid therein by means not shown or by other liquid mixing means, not shown, but which will now be obvious to those skilled in the art. The next step in the inventive method and system is to activate the vertical transport means such as cable 14 over pulley means 16 utilizing motor means not shown. Such activation picks up tray 12 and lifts it vertically including basket 10 resting thereon into rinse zone 18 of chamber 100. The tray and basket may be held at rest in zone 18 or may move continuously through zone 18 at a vertical speed sufficiently low to permit thorough rinsing of the objects contained in basket 10. Alternatively, electrically activated screw means or other vertical transport means (not shown) can provide close control of movement, up and down of the tray 12 and basket 10.

Preferably, rinse medium comprising relatively pure cleaning composition enters the system through conduit 48 and through a plurality of spray nozzles 26 spaced in vertical and circumferential relationship within zone 22. The spray rinse liquid falls from zone 22 as droplets 68 into the immersion liquid 20.

In a preferred embodiment, the tray 12 and basket 10 are raised into the uppermost portion of chamber 100 which comprises a drying zone 30. The drying fluid may be any inert non-toxic gaseous medium such as air or nitrogen. Preferably, such drying medium is heated by means, not shown to a temperature from 90-180^»F, typically, 120'F to 160'F. Preferably, and for safety reasons, the temperature is maintained 10'F to 20^λF below the flash point of the rinse medium. The drying medium enters the system through conduit 54 and control valve 60 from a source not shown. The gases are exhausted from chamber 100 to the atmosphere through opening(s) 66 at the top thereof. The tray and basket containing cleansed objects are removed from the system and put to intended use. Preferably, the gaseous medium in zone 30 is directed against the object by means, such as an air knife 28, vertically and/or circu ferentially disposed. The tray and basket may be held at rest in zone 30 or may move continuously therethrough. Drying times will vary depending upon the type of cleansing solution used for the immersion bath and the ambient temperature, and whether or not such medium is heated prior to entry into the system, i.e., time may vary from 1-2 minutes to 10-20 minutes, with 5-8 minutes being sufficient in most cases. The volume of gaseous drying medium will also be dependent upon the composition of the immersion cleaning solution, the ambient temperature, and the temperature of the drying medium itself. However, in all events, the volume of drying fluid should be an amount sufficient to act as a diluent to the vapors rising from within the chamber 100 by evaporation or otherwise. The diluting action of the drying medium significantly lessens the impact of atmospheric pollution on a volume percent basis. Typically, pollutants entering the atmosphere from operation of this invention method should be in the parts per million, e.g. 100-500 ppm vapor by volume which is at a level that is non-hazardous to the environment.

The rinse liquid in zone 18 falls as droplets 68 into bath 20 thereby raising the level of bath 20 above the draw pan means 32 of zone 22. The relatively impure cleaning solution is withdrawn from zone 22 through conduit 32 into distillation column 34. In column 34, the operating conditions are sufficient to separate the oil and grease contaminants from the cleansing solution which are withdrawn as waste through line 56 and control valve 58 to a disposal facility not shown. The relatively pure cleaning composition now devoid of at least a portion of the contaminants is withdrawn as a vapor through conduit 38, condensed in cooler 40, and collected in overhead receiver 42.

Condensed relatively pure cleaning solution in receiver 42 is withdrawn through conduit 44 with a portion being returned to column 34 as reflux through conduit 46. The other portion of relatively pure cleaning solution is passed through conduit 48, and pump 50 into zone 18 of chamber 100 as the relatively pure rinse medium. Make-up pure cleaning solution may be added as required through conduit 52 and control valve 49.

The operating conditions in column 34 may be atmospheric, super-atmospheric or sub-atmospheric. Thermal energy for distillation may be provided through reboiler 36 or any other means now known to those skilled in the art. In order to avoid thermal degradation and to minimize energy requirements of the cleaning solution, vacuum distillation of relative impure cleaning solution is preferred.

Accordingly, what is claimed is:

Claims

1. Method of degreasing the surface of solid objects which comprises the steps of:

(a) immersing a contaminated object in a liquid bath comprising a relatively impure solvent selective for the contaminants;

(b) removing the object from the immersion bath;

(d) contacting the object with a gaseous drying medium;

2. System for degreasing the surface of solid objects which comprises:

3. System according to claim 2 wherein the means for vertically transporting objects comprises an object container basket, resting on a tray support means movably connected to means suitable to vertical movement up and down, of the tray within the chamber.

4. System according to claim 3 wherein the chamber bath zone has associated therewith liquid agitation means.

5. System according to claim 3 wherein the means for vertical movement of the tray comprise electrically activated screw means.

6. System according to claim 3 including nozzle means for liquid rinse associated with the distillation zone and with the rinse zone.

7. System according to claim 6 including air knife means associated with the drying zone for supply of drying medium thereto.

8. A cleansing composition for removing contaminants from objects comprising:

(a) a alkane having from 5 to 20 carbon atoms per molecule, and,

(b) an aliphatic ester solvent having a flash point above 140^»F by Tag Closed Cup.

9. Cleaning composition of claim 8 wherein the alkane is branched-chain with a boiling range from 475^λF to 530'F and the ester is an oxoalcohol branched chain ester with a boiling range from 450 F to 550'F.

10. A degreaser solvent comprising a mixture of esters of low molecular weight aliphatic carboxylic acid and a normally liquid branched chain alkane.

11. Solvent according to claim 10 wherein the ester contains from 2 to 16 carbon atoms per molecule and the alkane is a mixture of isomers of dodecane.

12. Solvent according to claim 10 wherein the ester is an acetic acid ester having from 7 to 9 carbon atoms per molecule and having a boiling range from 340^»F to 420^λF and the alkane is an aliphatic hydrocarbon having from 10 to 14 carbon atoms per molecule and having a boiling range from 370'F to 410'F.

13. Solvent according to claim 10 wherein the ester is an acetic acid ester having from 9 to 11 carbon atoms per molecule and having a boiling range from 430^ to 480*F and the alkane is an aliphatic hydrocarbon having from 12 to 15 carbon atoms per molecule and having a boiling range from 430*F to 470^ΛF.

14. Solvent according to claim 10 wherein the ester is an oxoalcohol branched ester having from 11 to 14 carbon atoms, a flash point of at least 260^VF and a boiling range from 464*F to 545^λF; and the alkane is a branched chain paraffin having from 14 to 17 carbon atoms per molecule, a flash point of at least 240^F and a boiling range from 486^lF to 522'F.